Sub Floor Framing Question

[dog_and_ape]

Laying down 80 mil butyl and foil thermo-acoustic sound dampener over the sheet metal on the floor. I was originally thinking of laying down the sub-floor framing directly on top of the finished sheet metal with adhesive and screws and then place the sound mat in between the framing



I've had a thought now, though, that it might be better to lay the sound mat down over the entirety of the floor and then build the sub-floor on top of it.


Would there be any significant gain in sound/heat dampening from this extra step?


Would there be any problems with the structure of the sub-floor built on top of the sound mat versus directly onto the floor?


I'll be using spray foam insulation throughout the bus if that information is relevant.

[musigenesis]

Originally Posted by dog_and_ape

Laying down 80 mil butyl and foil thermo-acoustic sound dampener over the sheet metal on the floor. I was originally thinking of laying down the sub-floor framing directly on top of the finished sheet metal with adhesive and screws and then place the sound mat in between the framing



I've had a thought now, though, that it might be better to lay the sound mat down over the entirety of the floor and then build the sub-floor on top of it.


Would there be any significant gain in sound/heat dampening from this extra step?


Would there be any problems with the structure of the sub-floor built on top of the sound mat versus directly onto the floor?


I'll be using spray foam insulation throughout the bus if that information is relevant.

What's the PSI rating for the sound mat?

[Danjo]

I searched format and came across several brands. I don’t think I see what this will accomplish on the floor. It might knock down vibrational noise on a bare sheet metal floor, but I think that the addition of foam insulation, wood frame and plywood screwed to the floor kind of makes that stuff moot.

[TheHubbardBus]

Our tentative plan is to spray foam the entire interior, floor included.

Not only will it cost exactly the same as if we just did walls & ceiling (company we've chosen has a minimum square foot limit we're under even w/ the floor included), it should also provide significant sound deadening & it serves as its own vapor barrier.
If we weren't foaming the roof & walls, it might not be so cut & dried. But since we are, doing the floor at the same time seems to be a no-brainer. Nothing compares in the ability to kill so many birds (thermal/sound/vapor) with a single stone.

[wrenchtech]

Originally Posted by TheHubbardBus

...Nothing compares in the ability to kill so many birds (thermal/sound/vapor) with a single stone.

Makes a lot of sense to me.

[jsweet89]

Did you ever get a helpful response to this question? I’m at the same stage with the same question.

Did you install the kilmat across the entire floor and follow with the framing, or frame and then put kilmat and insulation within the framing spaces?

[IC08]

Originally Posted by jsweet89

Did you ever get a helpful response to this question? I’m at the same stage with the same question.

Did you install the kilmat across the entire floor and follow with the framing, or frame and then put kilmat and insulation within the framing spaces?

I would like to bump this thread, but its unlikely we will get a response. I'm just behind on putting in my subfloor so I'm trying to figure the same out.

check this out (if you haven't already)

https://www.skoolielivin.com/skoolie-subfloor/

they laid down something called "blue ridge fiber board premium insulating sheathing" to use as a sound/thermal barrier. Seemed like a good idea as they just liquid nails their 2x4's to that and it sounded easy. However when I emailed the manufacturer they said it can't withstand the psi for use in flooring -as its maid for walls/ceilings.

would love to find something like it, as we won't have radiant flooring and making sure our floor isn't cold in the winter is going to be top priority.

[jsweet89]

Thanks for responding. Discouraging about that manufacturer response.

My next step is to reach out to Kilmat and Dynamat directly for advice on this point — PSI and framing — since you’re at the same point I’ll reply here if/when I get a response.

[IC08]

Originally Posted by jsweet89

Thanks for responding. Discouraging about that manufacturer response.

My next step is to reach out to Kilmat and Dynamat directly for advice on this point — PSI and framing — since you’re at the same point I’ll reply here if/when I get a response.

Thanks, i found some online -kilmat is mostly sound barrier which at least in my case is less important than thermal, though it does have some insultaing ability. on amazon a 50sqft set is $62.

My bus interior is roughly 90x360 so if my math is correct..

EDIT: my math WAS trash lol

7.5 x 30 = 225sqft so thats 5 kits at $310 -not that bad actually

[LargeMargeInBaja]

2003, we converted a 1997 Ford CF8000 commercial truck to our concept of an ExpeditionVehicle.
.
After painting to seal the floor of the dry-van box, I laid one-inch pink-board.
Over that, I laid half-inch plywood, painted to seal all sides and surfaces.
.
Our visible floor is bamboo tongue-n-groove planks around the exterior with slate in the center.
.
Nearly two decades full-time live-aboard, across deserts and through rivers while bouncing along rough logger tracks, the pink-board shows no indication of deterioration or compression.
I would use this system again.
.
.
Our conversion took less than a week (and most of that time was waiting for paint to coagulate)... while selling everything.
I honestly truly believe 'SIMPLE IS BEST'.

[musigenesis]

Originally Posted by jsweet89

Thanks for responding. Discouraging about that manufacturer response.

My next step is to reach out to Kilmat and Dynamat directly for advice on this point — PSI and framing — since you’re at the same point I’ll reply here if/when I get a response.

Standard XPS foam board has a 20 PSI rating (give or take 5) which is more than adequate for building on top of without additional framing or "joists". It also provides decent acoustical insulation, especially in concert with a 3/4" layer of plywood on top.

[IC08]

Originally Posted by musigenesis

Standard XPS foam board has a 20 PSI rating (give or take 5) which is more than adequate for building on top of without additional framing or "joists". It also provides decent acoustical insulation, especially in concert with a 3/4" layer of plywood on top.

heard a "horror story" from one of the guys on youtube about how his dog's water bowl froze to the floor, and I think he did what I was planning which is wood framing with pink foam board inbetween the planks and ply on top. So at least in my case, I was wondering if an extra layer between the metal and wood might mitigate that. Especially because I'm going to rely solely on a wood stove for heat

Mostly I'm just shooting in the dark, but I figured overkill would be better than not. I noticed you went foam and ply.. ever test it in the single digits?

[musigenesis]

Originally Posted by IC08

heard a "horror story" from one of the guys on youtube about how his dog's water bowl froze to the floor, and I think he did what I was planning which is wood framing with pink foam board inbetween the planks and ply on top. So at least in my case, I was wondering if an extra layer between the metal and wood might mitigate that. Especially because I'm going to rely solely on a wood stove for heat

Mostly I'm just shooting in the dark, but I figured overkill would be better than not. I noticed you went foam and ply.. ever test it in the single digits?

Coldest I've been in was high 20s, and a 1500-watt electric space heater kept the temperature inside around 68°F, and the floor and ceiling were both that temperature as well. This was with all my windows uninsulated - I expect that with all the windows covered with my XPS inserts (once I've finished making them) and my 5kW diesel air heater going (once I've installed it), I'll be able to handle much lower temperatures. Single digits? I dunno, we'll see.

I expect your horror story about the frozen water bowl was because a lot of people do the thing where their framing is 2x4s or 1x4s on their sides. This results in a floor that has a higher proportion of wood than is necessary, and wood is a much worse insulator than XPS (XPS is R-5 per inch, wood is about R-1 per inch). The ideal floor from an insulation perspective is 0% wood and 100% foam. Mine is probably something like 2% wood (just from the supporting dowels) and 98% XPS.

The worst thing I ever saw (other than not insulating the floor at all) was a guy who made a criss-crossing grid of 1x6s spaced every 18" or so, with little squares of 3/4" XPS in the gaps. Something like that would be really awful in very cold weather.

Wood stoves can put out a lot of heat so you may not need to be super-worried about things. But in my mind it just makes sense to insulate as effectively as possible, regardless of your heat source.

[IC08]

Originally Posted by musigenesis

I expect your horror story about the frozen water bowl was because a lot of people do the thing where their framing is 2x4s or 1x4s on their sides. This results in a floor that has a higher proportion of wood than is necessary, and wood is a much worse insulator than XPS (XPS is R-5 per inch, wood is about R-1 per inch). The ideal floor from an insulation perspective is 0% wood and 100% foam. Mine is probably something like 2% wood (just from the supporting dowels) and 98% XPS.

You're pretty much blowing my mind right now as I'm reading your thread. The dowel thing was pretty snazzy, I think doing something similar to that is gonna be my ticket instead of an extra layer of something else

[jsweet89]

Originally Posted by musigenesis

The worst thing I ever saw (other than not insulating the floor at all) was a guy who made a criss-crossing grid of 1x6s spaced every 18" or so, with little squares of 3/4" XPS in the gaps. Something like that would be really awful in very cold weather.

I totally understand the issue with using one by sixes, which is why I’ve been thinking about using one by twos for framing the subfloor.

The attachment shows what I’ve been thinking. I live in Colorado, so in addition to noise reduction, insulation is very important. Curious if you think this is overkill. FYI we raised the roof by 1’ so not too worried about losing 2-3” height.

1x2 furring strips with 16-18” spaces between. Fill the spaces between furring strips with Kilmat and 3/4” XPS on top. On top of that layer is a layer of 1/2” Owens Corning foam insulation, then the plywood layer, and finally the top flooring.

Alternatively I’ve been thinking about doing electrical heater floor mats instead of the Owens Corning. (Electrical bc water looks painfully complicated for a beginner to figure out.)

Thank you very much.

[musigenesis]

Originally Posted by jsweet89

I totally understand the issue with using one by sixes, which is why I’ve been thinking about using one by twos for framing the subfloor.

The attachment shows what I’ve been thinking. I live in Colorado, so in addition to noise reduction, insulation is very important. Curious if you think this is overkill. FYI we raised the roof by 1’ so not too worried about losing 2-3” height.

1x2 furring strips with 16-18” spaces between. Fill the spaces between furring strips with Kilmat and 3/4” XPS on top. On top of that layer is a layer of 1/2” Owens Corning foam insulation, then the plywood layer, and finally the top flooring.

Alternatively I’ve been thinking about doing electrical heater floor mats instead of the Owens Corning. (Electrical bc water looks painfully complicated for a beginner to figure out.)

Thank you very much.

If the Kilmat can't be compressed on the bottom of your floor (and I don't see why it couldn't be since it seems to be basically rubber) and you need furring strips to keep it from being squashed, you can at least just run the furring strips every 18" or so in one direction only. There is no need to have them criss-crossing in order to provide adequate support for the top plywood layer. A lot of skoolie builders do the criss-crossing, but that doesn't achieve anything other than doubling the amount of wood in the floor.

Ideally, though, your floor would just be the Kilmat layer, then your insulation board (or boards), then tongue-and-groove plywood. The T&G aspect is important to keep your seams from separating and showing through the flooring layer above. Alternatively, you can just have furring strips underneath the plywood seams, giving you something to screw the edges into.

[IC08]

Originally Posted by jsweet89

Alternatively I’ve been thinking about doing electrical heater floor mats instead of the Owens Corning. (Electrical bc water looks painfully complicated for a beginner to figure out.).

I think the radiant floor thing is actually pretty easy imo. From what I've seen your hot water line just goes around in coils through your floor before it gets to the tap and because its nestled in insulation I don't think it would be a huge energy drain or make your hot water colder -but I haven't done it yet. I found all that on various youtubes. I'm still on the fence if it would be worth it.

Musigenesis really set me on a homework spree with the "ideal floor is 0% wood and 100% insulation" since then I've actually found lots of people saying the same thing and that framing it out is pretty pointless. One lady on fb just glued 2 inch owens corning to the metal, then plywood to that. Made it clear you really gotta go crazy with the glue, and weigh it down heavy for 24 hours. We might go that route, and I think maybe adding kilmat to the mix wouldn't change much. Still looking around though

[o1marc]

Originally Posted by IC08

I think the radiant floor thing is actually pretty easy imo. From what I've seen your hot water line just goes around in coils through your floor before it gets to the tap and because its nestled in insulation I don't think it would be a huge energy drain or make your hot water colder -but I haven't done it yet. I found all that on various youtubes. I'm still on the fence if it would be worth it.

It would only make your hot water colder if you have tanked water heater. The hydronic flooring needs an expansion chamber. I would not run the floor heat through my regular water supply. I have a tankless heater separate for the floor, and a second one for the house water. The floor is a sealed loop.

I laid a 1/2" layer of rigid board insulation, then laid a 1" layer and routed the lines for the PEX, heat spreaders, vapor barrier, and then the floor right on top.

[IC08]

Originally Posted by o1marc

It would only make your hot water colder if you have tanked water heater. The hydronic flooring needs an expansion chamber. I would not run the floor heat through my regular water supply. I have a tankless heater separate for the floor, and a second one for the house water. The floor is a sealed loop.

Ahh a separate system does make a bit more sense, did you go propane or electric? Is it pretty efficient?

[o1marc]

Originally Posted by IC08

Ahh a separate system does make a bit more sense, did you go propane or electric? Is it pretty efficient?

Propane, not completed yet, so no comment on efficiency. Separate heater for floor, and one for sink and shower.